High pressure shop air, or “HP air” is typically at about 125 psig pressure. Air is pressurized in a compressor and stored in a tank for operation in a range of, typically, 115 to 125 psig. HP air from the tank is piped throughout the plant as motive air for pneumatic equipment, or as pressurized air for purposes such as spraying or cleaning. While “high pressure” has to be high enough to meet all pressure requirements, some equipment operates at pressures lower than the “high pressure” level. For such lower pressure applications, a pressure reducing valve is required upstream of the equipment to reduce the pressure input to such equipment. A pressure reducing valve is a modulating orifice which allows high pressure air to expand to a lower pressure.
The problem with prior art systems as just described is that HP air is being wasted by putting it through a reducing valve to lower its pressure, wasting also the energy used to generate the HP air in the first place.
Factories often use many and various types of air driven equipment with varying requirements of air pressure and flow rate. The compressor and associated air tank are sized to meet the total pressure and volume requirements of all the pneumatic equipment in the factory. Pneumatic equipment typically takes in input air (or “Motive” air), and divides it into “Control” air and “Process” air. Control air controls equipment operation. Process air does the work. In an air-operated diaphragm pump, Control air operates an air direction control (DC) valve. The DC valve, in turn, directs Process air to drive the pump's diaphragm to thereby pump fluid. Control air and Process air then recombine, and together they exhaust from the pump to atmosphere.
It is an industry rule of thumb that a 2 psi change of output pressure corresponds with a 1% change of power required to generate it. Thus, the above-described reduction of HP air pressure from 125 psig to, say, 75 psig (a 50 psi reduction) represents a waste of 25% of the power required to generate it. In other words, 25% less power is required to compress air to 75 psig than is required to compress air to 125 psig. Another industry standard which will come into play here is that one horsepower is required to compress 4 cfm to 100 psig (i.e. 4 cfm/hp).
In addition to the term “high pressure” (HP), the terms “intermediate pressure” (IP) and “low pressure” (LP) may also be used herein, abbreviated as just indicated.
Pumps of the type described here are disclosed in U.S. Pat. No. 4,247,264 to Wilden.